In 3GPP (Third Generation Partnership Project), according to a radio communication system corresponding to LTE (Long Term Evolution) having a standard being currently designed, a radio base station eNB performs assignment of a radio resource in radio communication between the radio base station eNB and a radio terminal UE (for example, refer to Non Patent Literature 1). Furthermore, in the radio communication system corresponding to the LTE, one of frequency division duplex (FDD) and time division duplex (TDD) is employed in the radio communication between the radio base station eNB and the radio terminal UE.
Moreover, in an LTE (TDD-LTE) radio communication system employing the TDD, there has been discussed a feature where the radio base station eNB performs control (adaptive array control) for adaptively directing a beam toward the radio terminal UE that is moving at the time of transmission of a downlink radio signal and for directing a null toward another radio terminal UE, in order to ensure communication quality between the radio base station eNB and the radio terminal UE.
In the adaptive array control, a sounding reference signal (SRS) is transmitted from the radio terminal UE to the radio base station eNB using a resource block that is an uplink radio resource. Meanwhile, the radio base station eNB calculates an antenna weight for an uplink radio signal on the basis of the SRS.
However, the SRS is distributed and arranged in the frequency direction and the time direction. Therefore, in the calculation of an autocorrelation matrix in the process of calculating an antenna weight, there is a case in which SRS serving as an interference signal from another radio terminal is not added to SRS from one radio terminal UE and a null direction is not determined.